This invention relates to devices of recording and/or reproducing information on holographic storage medium.
It is desired that in the near future, optical disks will be enlarged in capacity to a level of 100 GB to 1 TB, that is, to the same level as a HDD (Hard Disk Drive).
However, in order to realize such a large capacity optical disk, it will be necessary to develop a new storage technology different from the past trend of high-density technology as indicated by the use of shorter wavelength and higher NA objective lenses.
Holographic recording is a promising technology for future optical data storage with larger capacity and higher transfer rate.
In the holographic technology, data information is recorded through interference patterns of signal beam modulated two-dimensionally by a spatial light modulator and reference beam in holographic storage medium.
And data information is reproduced two-dimensionally by means of CMOS, CCD, and other photo detectors
These features are effective for large-capacity, high-speed recording and reproduction of information.
The hologram recording technology is referred to, for example, in Japanese Patent Application Laid-open Publication No. 2004-272268-A (Patent Document 1) and Non-Patent Document 1. These documents carry descriptions about the so-called angular multiplexing recording method. Furthermore, the same Patent Document 1 also describes a technology that can make array distances between adjoining holograms narrower by placing a spatial filter (polytopic filter) at the beam waist of the signal beam and can increase recording density and capacity as compared with the conventional angular multiplexing recording method.
The hologram recording technology is also taken up, for example, in WO 2004-102542 (Patent Document 2). This Patent Document 2 describes an example about shift multiplexing method. In this method, hologram is recorded by interference of signal beam from the inner pixels in a spatial light modulator and reference beam from the outer pixels in the ring-belt shape zone in the same modulator.
Another related art is also found in Japanese Patent Application Laid-open Publication No. 11-311938-A (Patent document 3). This Patent Document 3 discloses an example about cure system to cure a recorded hologram.    [Patent Document 1] Japanese Patent Application Laid-open Publication No. 2004-272268-A    [Patent Document 2] WO 2004-102542    [Patent Document 3] Japanese Patent Application Laid-open Publication No. 11-311938-A    [Non-patent Document 1] “The InPhase Professional Archive Drive OMA; Design and Function,” Ian Redmond; Optical Data Storage Topical Meeting 2006.